If non-chlorine shock doesn’t cut it, you go old school. You need to raise your free chlorine level to at least 10 times the combined chlorine level. It’s called “breakpoint chlorination” and it sounds fancy, but it’s just math.
Test your water. Find the combined chlorine number. Multiply it by 10. Add that many ppm of chlorine shock. Your pH should be between 7.2 and 7.4 for this to work—otherwise, the chlorine just sits there like a grumpy teenager.
This is the “burn it all down” approach. You’re essentially throwing so much chlorine at the problem that the contaminants have no choice but to surrender. Your pool will smell like a laundromat for a day, but that’s the price of victory.
